In recent years, for the reduction in cost and thickness of a camera module which is mounted on a mobile terminal, the number of lenses is decreased and lenses having a low MTF (modulation transfer function) characteristic are employed. In order to cover the insufficient focusing due to the low MTF, for example, an edge correction (an edge enhancement process) is performed through a digital signal process. In general, the edge enhancement process is performed such that a predetermined band of edge components extracted by a bandpass filter (BPF) is subjected to a predetermined process and edge portions are added with an overshoot effect or an undershoot effect.
Particularly, in a case of an image having a low signal-to-noise ratio (SNR), noise components are extracted along with the edge components and are added to the edge portions, so that the SNR of the obtained image is degraded further more. The degradation in the SNR is dealt with by adding a noise cancelling function to the extracted edge component. The noise cancelling function also causes the decrease of the edge components as well as the noise components. For this reason, with the application of the noise cancelling function, resolution may be lowered under a desired level.
Since the amplitudes of the edge components are large in a bright part and small in a dark part, a necessary level of edge enhancement varies according to light and dart. Regarding an image containing the bright part and the dark part as well, it is preferable that the edge enhancement process be strongly performed with respect to the bright part but weakly to the dark part. In addition, the edge in the bright part is subjected to an amplitude limitation process of clipping the edge enhancement on a desired level in order to keep a balance at the level of the edge enhancement.
In a case where the balance at the level of the edge enhancement takes priority, the level for limiting the edge enhancement is set to be low, so that the edge enhancement is insufficiently made. In this regard, actions can be taken to increase the level of the edge enhancement by multiplying the edge component after the amplitude limitation process by a gain. In this case, the noise contained in the edge components which are extracted from the dark part is amplified as well. On the contrary, in a case where the limiting level of the edge enhancement is set too high, the balance at the level of the edge will be lost. In this way, according to the related art, the effective adjustment for the edge enhancement and the noise suppression may be difficult.